Temperature compensation for an oscillator crystal

ABSTRACT

An electronic device is equipped with an oscillator interface to be coupled to an oscillator crystal of an oscillator element. The electronic device includes an oscillator circuit which is coupled to the oscillator interface and generates an oscillator signal. The electronic device is further provided with a temperature measurement interface to be coupled to a temperature sensor of the oscillator element so as to receive the temperature signal. For accomplishing temperature compensation, the electronic device is provided with a measurement controller coupled to the measurement interface and configured to measure a first value of the temperature signal at a first point of time and a second value of the temperature signal at a second point of time. A frequency drift estimator is provided so as to estimate a frequency drift of the oscillator signal on the basis of the first value of the temperature signal and a second value of the temperature signal. By means of a compensation logic, a frequency compensation signal for the oscillator circuit is generated on the basis of the estimated frequency drift.

FIELD OF THE INVENTION

The present invention relates to techniques of temperature compensationfor an oscillator crystal.

BACKGROUND OF THE INVENTION

In electronic devices, it is known to use oscillator crystals for thepurpose of generating an oscillator signal. For example, such anoscillator signal may be used as a basis for operating a radio frequency(RF) receiver, e.g. in a mobile communication system or in a positioningdevice.

For some applications, the oscillator signal is required to have ahighly stable frequency. Examples of such applications are evolvedmobile communication systems, such as mobile communication systemsaccording to the UMTS (Universal Mobile Telecommunications System), orsatellite-based positioning systems, such as GPS (Global PositioningSystem).

However, conventional oscillator crystals typically do not provide therequired frequency stability. In particular, the frequency may varyalong with the temperature of the oscillator crystals.

BRIEF SUMMARY OF THE INVENTION

In an embodiment, an electronic device is provided. The electronicdevice comprises an oscillator interface and a temperature measurementinterface. Further, the electronic device comprises an oscillatorcircuit, a measurement controller, a frequency drift estimator, and acompensation logic. The oscillator interface is to be coupled to anoscillator crystal of an oscillator interface, and the temperaturemeasurement interface is to be coupled to a temperature sensor of theoscillator element so as to receive a temperature signal. The oscillatorcircuit is coupled to the oscillator interface and is configured togenerate an oscillator signal. The measurement controller is coupled tothe temperature measurement interface and is configured to measure afirst value of the temperature signal at a first point of time and asecond value of the temperature signal at a second point of time. Thefrequency drift estimator is configured to estimate a frequency drift ofthe oscillator signal on the basis of the first value of the temperaturesignal and the second value of the temperature signal. The compensationlogic is configured to generate a frequency compensation signal for theoscillator circuit on the basis of the estimated frequency drift.

It is to be understood that the above summary is only intended toprovide an abbreviated overview of some features of some embodiments ofthe present invention and is not to be construed as limiting. Inparticular, other embodiments may comprise features, more featuresand/or alternative features.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 schematically illustrates an electronic device according to anembodiment of the invention.

FIG. 2 shows a flow chart for schematically illustrating a methodaccording to an embodiment of the invention.

FIG. 3 schematically illustrates an oscillator circuit according to anembodiment of the invention.

FIG. 4 schematically illustrates a multi-device implementation of anelectronic device according to an embodiment of the invention.

FIG. 5 shows a block diagram for schematically illustrating functions inan electronic device according to an embodiment of the invention.

FIG. 6 shows an exemplary temperature characteristic of an oscillatorcrystal as used in an embodiment of the invention.

FIG. 7 shows exemplary simulation results representing the frequencyerror of an oscillator signal as a function of time when applying atemperature gradient.

FIG. 8 shows exemplary simulation results representing the frequencydrift of an oscillator signal as a function of time when applying atemperature gradient.

In the following, some embodiments of the present invention will bedescribed in more detail and with reference to the accompanyingdrawings. It is to be understood that the following description is givenonly for the purpose of illustration and is not to be taken in alimiting sense. The scope of the invention is not intended to be limitedby the embodiments as described hereinafter, but is intended to belimited only by the appended claims.

Further, it is to be understood that in the following description ofembodiments any direct connection or coupling between functional blocks,devices, components, circuit elements or other physical or functionalunits as described or shown in the drawings could also be implemented byan indirect connection or coupling, i.e. a connection or couplingcomprising one or more intervening elements. Furthermore, it should beappreciated that functional blocks or units shown in the drawings may beimplemented as separate circuits, but may also be fully or partiallyimplemented in a common circuit. In other words, the description ofvarious functional blocks is intended to give a clear understanding ofvarious functions performed in a device and is not to be construed asindicating that these functional blocks have to be implemented asseparate functional units. For example, one or more functional blocksmay be implemented by programming a processor with suitably designedprogram code.

It should be noted that the drawings are provided to give anillustration of some aspects of embodiments of the present invention andtherefore are to be regarded as schematic only. In particular, theelements as shown in the drawings are not necessarily to scale with eachother, and the placement of various elements and drawings is chosen toprovide a clear understanding of the respective embodiment and is not tobe construed as necessarily being a representation of the actualrelative location of the illustrated structures.

It is to be understood that the features of the various embodimentsdescribed herein may be combined with each other as appropriate. On theother hand, describing an embodiment with a plurality of features is notto be construed as indicating that all the described features arenecessary for practicing the present invention. For example, otherembodiments may comprise less features and/or alternative features.

Turning now to the figures, FIG. 1 schematically illustrates anelectronic device 100 according to an embodiment of the presentinvention. The electronic device 100 may be implemented using one ormore integrated circuits, possibly in combination with additionalelements like resistors, capacitors, antennas, or the like. As furtherillustrated, the electronic device 100 is coupled to an oscillatorelement 10. The oscillator element 10 comprises an oscillator crystal12.

Further, the oscillator element 10 comprises a temperature sensor 14,e.g. a temperature-sensitive diode or resistor. Thermal coupling of thetemperature sensor 14 to the oscillator crystal 12 may be accomplished,e.g. by placing the temperature sensor 14 in vicinity of the oscillatorcrytal 12, by connecting the temperature sensor 14 to the oscillatorcrytal 12 via a heat conducting material, such as thermal grease or thelike, by placing the temperature sensor 14 and the oscillator crytal ina common housing or package, or any combination therof. In someembodiments, the temperature sensor 14 may be a resistor with a negativetemperature coefficient, sometimes also referred to as a NTC resistor.In the illustrated example, the temperature sensor is illustrated aswith one terminal coupled to a given ptential, e.g. ground, while theother terminal is available for receiving a probe signal and/orextracting a temperature signal. Such a configuration may be used, e.g.,if the temperature sensor 14 is a resistor. However, it is to beunderstood that, depending on the type of the temperature sensor 14, thetemperature sensor 14 may be connected in other configurations. Theoscillator element 10, which inludes the oscillator crystal 12 and thetemperature sensor 14, may be implemented as a “system in package”(SiP).

The electronic device 100 comprises an oscillator circuit 110. Theoscillator circuit 110 is configured to generate an oscillator signalOSC, which may have various signal forms, e.g. sinusoidal, trapezoidal,rectangular. The oscillator signal may also have the form of a digitalclock signal. In some embodiments, the oscillator circuit 110 may beconfigured as a frequency synthesizer circuit. In further embodiments,the oscillator circuit may be configured as a clock generator circuit.The oscillator circuit 110 may comprise various types of oscillatorcircuitry suitable for coupling to the oscillator crystal 12, e.g. ananalog reference oscillator. Such oscillator circuitry may be composedof resistors, capacitors, transistors, or the like. Moreover, theoscillator circuit 110 may comprise a phase-locked-loop (PLL), e.g. anN-fractional PLL, and/or a signal shaper configured to output theoscillatory signal with a desired signal form, e.g. as a digital clocksignal switching between two binary values.

In the illustrated example, the oscillator circuit 110 is coupled to theoscillator element 10 via an oscillator interface of the electronicdevice 100, which is provided by terminals 22, 23. By using theoscillator interface, the oscillator element 10 with the oscillatorcrystal 12 may be located spaced apart from the electronic device 100,which reduces temperature variation of the oscillator crystal 12 due toheat generated by the electronic device 100.

As further illustrated, the electronic device 100 comprises terminals24, 25 for coupling to the temperature sensor 14 of the oscillatorelement 10. The terminals 24, 25 implement a temperature measurementinterface of the electronic device 100. Via the temperature measurementinterface, the electronic device 100 may receive a temperature signal TSfrom the temperature sensor 14.

In the illustrated example, the temperature signal TS is an analogsignal and the electronic device 100 comprises an analog-to-digitalconverter (ADC) 120 for converting the temperature signal TS to adigital signal. Further, the electronic device 100 comprises a probesignal source 125, which is configured to supply a probe signal PS tothe temperature sensor 14 of the oscillator element 10. According to anembodiment, the probe signal PS is a current, and the temperature signalTS is a voltage generated at the temperature sensor 14.

It is to be understood, that other types of temperature signals areconceivable as well. For example, the temperature signal TS may be adigital signal, e.g. generated by an ADC in the oscillator element 10,or a current. Depending on the type of the temperature signal TS and theimplementation of the temperature measurement in the oscillator element10, the ADC 120 and/or the probe signal source 125 of the electronicdevice 100 may be omitted or replaced by other elements.

The electronic device.100 further comprises a measurement controller140. The measurement controller 140 is configured to controlmeasurements of the temperature signal TS. In particular, themeasurement controller 140 is configured to measure at least a firstvalue of the temperature signal TS at a first point of time and a secondvalue of the temperature signal TS at a second point of time. Accordingto one implementation, the measurement controller 140 may repeatedlymeasure the value of the temperature signal TS at regular timeintervals, thereby continuously generating new pairs of first and secondvalues. As used herein, the first and second values may be any pair ofvalues measured at different points of time, e.g. two subsequentlymeasured values. For performing the measurements, the measurementcontroller 140 suitably controls the ADC 120 and/or the probe signalsource 125. In the following explanations, the first value of thetemperature signal is referred to as T₁, and the second value of thetemperature signal is referred to as T₂.

As further illustrated, the electronic device 100 comprises a frequencydrift estimator 150, and a frequency error estimator 160. The measuredvalues of the temperature signal TS, i.e. the first temperature signalvalue T₁ and the second temperature signal value T₂, are supplied to thefrequency drift estimator 150 and the frequency error estimator 160.

The frequency drift estimator uses the values T₁ and T₂ for estimating afrequency drift of the oscillator signal OSC. This may be accomplishedusing a stored temperature characteristic of the oscillator signalfrequency as stored in a temperature characteristic memory 180 of theelectronic device 100. The temperature characteristic relates a value ofthe temperature signal to a corresponding value of the frequency of theoscillator signal OSC. Here, it is to be understood that the frequencymay also be expressed as a frequency error, i.e. the deviation of thefrequency from a nominal frequency. In FIG. 1, the value of thefrequency corresponding to a value T of the temperature signal isdenoted by f_(s)(T). The temperature characteristic may be stored in theform of paramters of an approximating function to the temperaturecharacteristic. For example, the approximating function may be apolynomial of at least third order and the stored parameters may becoefficients of the polynomial. According to other implementations,other approximating functions may be used, e.g. a polynomial of fourthor higher order, a Lagrange approximation, or a Spline approximation.Moreover, the temperature characteristic could also be stored in theform of a look-up table.

In one embodiment, the frequency drift estimator may use a differencebetween the first value T₁ of the temperature signal and the secondvalue T₂ of the temperature signal and/or a difference between a firstfrequency value f(T₁) corresponding to the first temperature signalvalue and a second frequency value f(T₂) corresponding to the secondtemperature signal value for calculating the estimated frequency drift.According to one implementation, the estimated frequency drift may becalculated according to

$\begin{matrix}{\left( {\Delta \; {f/\Delta}\; t} \right)_{E} = \frac{{f\left( T_{2} \right)} - {f\left( T_{1} \right)}}{T_{2} - T_{1}}} & (1)\end{matrix}$

Here, it is to be noted that the frequency values used in thecalculation may be obtained from the stored temperature characteristic,i.e. may be the values f_(s)(T). However, in some situations alsoevaluated frequency values may be available and may be used in thecalculation of the estimated frequency drift. This will be furtherexplained below.

The frequency error estimator 160 is configured to estimate a frequencyerror Δf of the oscillator signal OSC. This may be accomplished usingthe first temperature signal value T₁ and/or the second temperaturesignal value T₂ and the stored temperature characteristic. Inparticular, the frequency error estimator 160 may use the temperaturesignal value to obtain the corresponding frequency value f_(s)(T)according o the stored temperature characteristic, which may in turn beused to calculate the deviation from a nominal frequency. In somesituations, the frequency error Δf may also be determined from anevaluated frequency value, without using the stored temperaturecharacteristic.

The electronic device 100 further comprises a compensation logic 170which receives at least the estimated frequency drift (Δf/Δt)_(ε) fromthe frequency drift estimator 150. According to an embodiment, thecompensation logic 170 may further receive the estimated frequency errorΔf from the frequency error estimator 160. The compensation logic 170 isconfigured to generate frequency compensation signal on the basis of theestimated frequency drift (Δf/Δt)_(ε), and optionally also on the basisof the estimated frequency error Δf. According to an embodiment, thefrequency compensation signal may be generated so as to correspond to afrequency drift which has an inverse characteristic of the estimatedfrequency drift. For this purpose, a value of the frequency compensationsignal may be increased or decreased at a rate which is proportional tothe estimated frequency drift. The frequency compensation signal isapplied to the oscillator circuit 110 so as to compensatetemperature-induced variations of the frequency of the oscillator signalOSC. Using the estimated frequency drift (Δf/Δt)_(ε) as a basis forgenerating the frequency compensation signal allows for stabilizing thefrequency in a very efficient manner.

As further illustrated, the electronic device 100 comprises a processingmodule 200 which is configured to operate on the basis of the oscillatorsignal OSC. The processing module 200 may be a positioning module, e.g.a GPS module, or may be a mobile communication module, e.g. according tothe UMTS standard. In the processing module 200, the oscillator signalOSC may be used for processing received high-frequency signals, e.g.positioning signals received from satellites or wireless communicationsignals received from a base station. In a mobile communicationscenario, the oscillator signal OSC may also be used in the process oftransmitting signals to the base station.

Among other functions related to the specific purpose of the processingmodule 200, the processing module 200 may also be configured to evaluateparameters of the oscillator signal OSC. In particular, the processingmodule 200 may evaluate the frequency of the oscillator signal OSC. Ifthe processing module 200 is a positioning module, the frequency f maybe evaluated-on the basis of a position fix. If the processing module200 is a mobile communication module, the frequency f may be evaluatedfrom synchronization with a base station. Other parameters of theoscillator signal OSC may be evaluated as well, e.g. a frequency drift,or an uncertainty of the evaluated frequency drift. In some embodiments,the processing module 200 may also comprise a positioning sub-module anda mobile communication sub-module. In such a scenario, the mobilecommunication sub-module could deliver a synchronized oscillator signalof known frequency, which is obtained from synchronization with a basestation, to the positioning sub-module, which then compares theoscillator signal to the synchronized oscillator signal so as toevaluate the parameters of the oscillator signal, e.g. frequency,frequency error, frequency drift, uncertainty of the evaluated frequencydrift.

The evaluated parameters of the oscillator signal OSC may be used forvarious purposes. In the illustrated example, the electronic device 100comprises an update logic 190 which is supplied with the evaluatedfrequency f and/or other parameters of the oscillator signal OSC. Theupdate logic 190 further receives the measured value of the temperaturesignal TS. On the basis of these values, the update logic 190 may adaptthe temperature characteristic as stored in the temperaturecharacteristic memory 180. In this way, the accuracy of the storedtemperature characteristic may be improved. Further, aging of theoscillator crystal 12 may be taken into account.

FIG. 2 shows a flow chart for schematically illustrating a method oftemperature compensation according to an embodiment of the invention.The method may be implemented in an electronic device as illustrated inFIG. 1.

At step 210, an oscillator signal is generated, e.g. by the oscillatorcircuit 110 as illustrated in FIG. 1. For this purpose, the oscillatorcircuit is coupled to an oscillator crystal, e.g. the oscillator crystal12 of the oscillator element 10 as illustrated in FIG. 1.

At step 220, a temperature signal representing the temperature of theoscillator crystal is obtained. As explained in connection with FIG. 1,the temperature signal may be an analog voltage generated at atemperature sensor, e.g. a NTC resistor or the like. The temperaturesensor may be placed together with the oscillator crystal in anoscillator element, e.g. in a single electronic device package. Forgenerating the temperature signal, a probe signal may be supplied to thetemperature sensor, e.g. a probe current.

At step 230, a first value of the temperature signal is measured at afirst point of time, and a second value of the temperature signal ismeasured at a second point of time. These measurements may be controlledby the measurement controller 140 as illustrated in FIG. 1 and mayinvolve converting the analog temperature signal to digital values, e.g.by the ADC 120 as illustrated in FIG. 1, and supplying a probe signal tothe temperature sensor, e.g. by the probe signal source 125 asillustrated in FIG. 1. For accomplishing the measurements, themeasurement controller may suitably set parameters of the ADC 120 and/orof the probe signal source 125. For example, the probe signal source 125may be controlled to supply the probe signal only during samplingintervals of the ADC 120, thereby avoiding unnecessary heat generationat the temperature sensor and reducing power consumption.

At step 240, a frequency drift the oscillator is estimated on the basisof the measured first and second values of the temperature signal. Thismay be accomplished by the drift estimator 150 as illustrated in FIG. 1.As explained above, the frequency drift may be estimated on the basis ofa stored temperature characteristic of the oscillator signal frequency.The temperature characteristic may be stored in a corresponding memory,e.g. the temperature characteristic memory 180 as illustrated in FIG. 1.The temperature characteristic may be stored in the form of coefficientsof an approximating function to the temperature characteristic. Theapproximating function may be a polynomial of at least third order orany other kind of approximating function. Using the stored temperaturecharacteristic, frequency values corresponding to the measured first andsecond values of the temperature signal may be obtained and used forcalculating the estimated frequency drift. In particular, estimating thefrequency drift may involve calculating a difference between the firstvalue of the temperature signal and the second value of the temperaturesignal and/or calculating a difference between a first frequency valuecorresponding to the first value of the temperature signal and a secondfrequency value corresponding to the second value of the temperaturesignal. According to one implementation, the estimated frequency driftmay be calculated in the above-described manner using equation (1). Inaddition or as an alternative to using a stored temperaturecharacteristic for obtaining the frequency values corresponding to themeasured values of the temperature signal, frequency values may be usedwhich have been evaluated from the oscillator signal. For example, thefrequency values may be evaluated from a position fix obtained by apositioning module operating on the basis of the oscillator signaland/or from synchronization with a base station as accomplished by themobile communication module operating on the basis of the oscillatorsignal.

In addition to estimating the frequency drift, also a frequency errormay be estimated on the basis of the first and/or the second measuredvalues of the temperature signal. For estimating the frequency error ofthe oscillator signal, the measured value of the temperature signal maybe used in connection with the stored temperature characteristic.Further, a frequency error may also be estimated from frequency valueswhich have been evaluated from the oscillator signal in theabove-mentioned manner, e.g. from a position fix or from synchronizationwith a base station.

At step 250, a frequency compensation signal for the oscillator circuitis generated at least on the basis of the estimated frequency drift.This may be accomplished by the compensation logic 170 as illustrated inFIG. 1. The compensation signal may be a control signal for a digitalPLL of the oscillator circuit. For example, the frequency compensationsignal may control an N-fractional divider of the PLL. Using thefrequency compensation signal, the frequency of the oscillator signalmay be controlled so as to counteract the frequency drift. In thismanner, the frequency of the oscillator signal may be stabilized in avery effective manner.

FIG. 3 schematically illustrates an exemplary implementation of theoscillator circuit 110.

As illustrated, the oscillator circuit 110 comprises a referenceoscillator 112 which is coupled to the oscillator crystal 12. Thereference oscillator may be implemented using a known type of oscillatorcircuitry. The reference oscillator outputs a reference oscillatorsignal REF.

The oscillator circuit 110 further comprises a PLL 114 operating on thebasis of the reference oscillator signal REF. According to theillustrated example, the PLL is implemented as an N-fractional PLL andcomprises an N-fractional divider 116. The N-fractional divider may bearranged in a feedback path of the PLL. Due to the N-fractional divider,the oscillator signal OSC as generated by the oscillator circuit 110 hasa frequency f which corresponds to the frequency of the referenceoscillator signal REF multiplied by a divider N_(fractional) of theN-fractional divider 116.

As illustrated, the compensation logic 170 supplies the frequencycompensation signal to the oscillator circuit 110 in the form of a PLLcontrol signal PLLctrl, which is used to adjust the dividerN_(fractional) of the N-fractional divider 116 in the PLL 114. In thisway, the frequency of the oscillator signal OSC may be digitallycontrolled in a precise and efficient manner. In addition or as analternative, the frequency compensation signal may also be supplied tothe oscillator circuit 110 in the form of a reference oscillator controlsignal OSCctrl, which causes the reference oscillator 112 to adapt isoperation. In the latter case, the freqency compensation signal may beused to control the frequency of the reference oscillator signal REF.

It is to be understood that the control mechanism on the basis ofadjusting the N-fractional divider and/or the reference oscillator asillustrated in FIG. 3 is only one example of adapting the oscillatorcircuit 110 so as to accomplish temperature compensation. For example,the freuquency compensation signal could also be used to control othercomponents of the PLL and/or the oscillator circuit 110 may comprisefurther components which are adjustable on the basis of the frequencycompensation signal.

FIG. 4 schematically illustrates a multi-device implementation of theelectronic device 100 as described in connection with FIG. 1. In theillustrated example, the electronic device 100 comprises a signalprocessing device 410 and a host processing device 430 which are coupledto each other via a host interface 420. The signal processing device 410may be implemented by a corresponding integrated circuit, and the hostprocessing device 430 may be implemented by a corresponding integratedcircuit.

The signal processing device 410 and the host processing device 430 maytogether implement the functions of the electronic device 100 asillustrated in FIG. 1. It is to be understood that the functions may bedistributed among the signal processing device 410 and the hostprocessing device 430 in various manners. For example, the signalprocessing device 410 may comprise the oscillator circuit 110, the ADC120 and the probe signal source 125. Further, the signal processingdevice 410 may also comprise a part of the processing module 200, a partof the compensation logic 170, and/or a part of the measurementcontroller 140. These elements may be implemented by hardware of thesignal processing device and/or firmware of the signal processing device410.

The host processing device 430 may in turn comprise the frequency driftestimator 150, the frequency error estimator 160, the temperaturecharacteristic memory 180, the update logic 190, and at least a part ofthe measurement controller 140, at least a part of the compensationlogic 170, and at least a part of the processing module 200. Theseelements may be implemented by software executed by a processor of thehost processing device 430.

According to one example, the electronic device 100 implementspositioning functions, e.g. using GPS or other satellite-basedpositioning system. In such a case, the signal processing device 410 maybe adapted for accomplishing processing of received positioning signals,such as down-conversion of received positioning signals from RF signalsto base-band signals, analog-to-digital conversion, code-correlation, orthe like. The host processing device 430 may in turn implement apositioning engine which accomplishes evaluation of the receivedpositioning signals so as to obtain a position fix. According to anotherexample, the electronic device 100 implements mobile communicationfunctions. In such a case, the signal processing device 410 may beadapted to perform signal processing of received and/or transmittedcommunication signals, such as demodulation, down-conversion from RFsignals to base-band signals, analog-to-digital conversion, decoding, orthe like. The host processing device 430 may then in turn accomplishhigher-level communication functions, such as data processing accordingto specific communication protocols or the like.

FIG. 5 shows a block diagram for schematically illustrating animplementation of the electronic device according to the above-mentionedGPS scenario. As illustrated, functions of the electronic device may beassigned to a number of functional blocks which comprise a core GPSengine 510, GPS engine compensation functions 520, GPS engine callbackfunctions 530, signal processing firmware 540, and signal processinghardware 550. Assuming the device structure as illustrated in FIG. 4,the core GPS engine 510, the GPS engine compensation functions 520, andthe GPS engine callback functions 530 may be implemented by the hostprocessing device 430, whereas the signal processing firmware 540 andthe signal processing hardware 550 may be implemented by the signalprocessing device 410.

The core GPS engine 510 may implement functions such as frequencyevaluation on the basis of a predicted frequency change, frequencyevaluation on the basis of a position fix, frequency drift evaluation onthe basis of a predicted frequency change, frequency drift evaluation onthe basis of a position fix, or evaluation of an uncertainty of theevaluated frequency or frequency drift. These results, i.e. theevaluated frequency f, the evaluated frequency drift Δf/Δt, and or theother evaluated parameters, may also be passed to the GPS enginecompensation function 520.

The GPS engine compensation functions 520 may implement functions suchas providing temperature characteristic data, e.g. by approximating thetemperature characteristic as a polynomial of third or higher order,calculating temperature values representing the oscillator crystaltemperature on the basis of an ADC output signal, estimating thefrequency, the frequency error, and/or the frequency drift on the basisof the temperature values and the stored temperature characteristic, andgenerating the frequency compensation signal at least, on the basis ofthe estimated frequency drift. The GPS engine compensation functions 520may also predict a frequency change Δf_(ε), which may be supplied to thecore GPS engine 510.

As illustrated, the GPS engine compensation functions 520 communicatewith the signal processing firmware 540 via the GPS engine callbackfunctions 530. In particular, the GPS engine compensation functions 520communicate the frequency compensation signal, in the form of the PLLcontrol signal PLLctrl, and an ADC control signal ADCctrl to the signalprocessing firmware 540 and the signal processing firmware 540communicates the ADC output signal ADCout to the GPS engine compensationfunctions 520 via the GPS engine callback functions 530.

Among other known signal processing functions, the signal processingfirmware 540 implements functions such as configuration of the ADC 120,reading values of the ADC at the desired points of time, and generatingthe frequency compensation signal, in the form of the PLL control signalPLLctrl to be supplied to the PLL of the oscillator circuit 110. Here,it is to be understood that the GPS engine compensation function maygenerate the PLL control signal PLLctrl at a lower update rate than thesignal processing firmware 540. For example, the GPS engine compensationfunction may generate the PLL control signal PLLctrl at an update rateof a few seconds, e.g. about 1 s, whereas the signal processing firmware540 may generate the PLL control signal PLLctrl at an update rate of afew milliseconds, e.g. about 1 ms. Since the PLL control signal PLLctrlis generated on the basis of the estimated frequency drift, the signalprocessing firmware 540 is able to perform a precise interpolationbetween the values as provided by the GPS engine compensation functions520.

The signal processing firmware 540 delivers the measured values of thetemperature signal, i.e. the ADC output signal ADCout, to the GPS enginecompensation functions 540, which is accomplished via the GPS enginecallback functions 530. Further, the signal processing firmware 540supplies the PLL control signal PLLctrl and the ADC control signalADCctrl to the signal processing hardware 550.

Among other signal processing functions, the signal processing hardware550 may comprise an ADC for accomplishing analog-to-digital conversionof the temperature signal, e.g. the ADC 120. Further, the signalprocessing hardware 550 may accomplish averaging of ADC values. In thisway, the ADC output signal ADCout is generated. In addition, the signalprocessing hardware 550 comprises the oscillator circuit with the PLLconfigured to be adapted on the basis of the PLL control signal PLLctrl,e.g. the oscillator circuit 110.

The signal processing hardware 550 supplies the ADC output signal, i.e.the values as obtained by analog-to-digital conversion of thetemperature signal and optionally averaging, to the signal processingfirmware 540.

It is to be understood that the functions as explained in connectionwith FIG. 5 and their arrangement are merely exemplary and that otherfunctions could be implemented and/or the functions could be assigned tothe functional blocks in a different manner.

FIG. 6 shows a diagram representing an exemplary temperaturecharacteristic of an oscillator crystal, e.g. the oscillator crystal 12as shown in FIG. 1. Specifically, FIG. 6 shows a frequency error Δf as afunction of the temperature T. In the illustrated example, thetemperature characteristic is approximated by a third order polynomial.

In the figure, a straight solid line illustrates the gradient df/dT ofthe temperature characteristic at 0° C., whereas a straight dashed lineillustrates the frequency drift Δf/Δt as estimated according to theabove-mentioned concepts. As can be seen, both the gradient and theestimated frequency drift can be used to predict the further course ofthe frequency error Δf and therefore be used as a basis for efficientlycompensating frequency variations due to changes in the temperature.

FIG. 7 shows exemplary simulation results representing the frequencyerror Δf as a function of time, denoted by t, during a temperature rampof 10° C./min when implementing temperature compensation according tothe above-described concepts. As can be seen, the frequency of theoscillator signal can be stabilized so as to limit frequency variationsto significantly less than 1 ppm.

FIG. 8 shows simulation results representing the frequency drift Δf/Δtas a function of time during a temperature ramp of 10° C./min whenapplying the above-described concepts of temperature compensation. Ascan be seen, the frequency drift is controlled in an efficient mannerand is typically kept in the range of a few ppb/s.

It should be noted that the numerical values of the simulation resultsas shown in FIGS. 7 and 8 serve only for the purpose of furtherillustrating the concepts according to some embodiments of the presentinvention and are not to be construed as limiting.

It is to be understood that the above-described embodiments serve onlyas examples for implementations of concepts according to the presentinvention, and that these concepts may be applied in various mannerswhich are not restricted to the described embodiments. For example, theconcepts of temperature compensation as described herein may be appliedin other systems than positioning systems or mobile communicationsystems. Moreover, the above-described embodiments are susceptible tovarious modifications. For example, the frequency compensation signalmay not only be generated on the basis of the estimated frequency driftor frequency error, but may also be generated taking into accountfurther parameters, such as temperature overshoot in dependence of achange in temperature or activity dips, which may cause temporaldeviations of the frequency drift. Also, it is to be understood that thetemperature characteristic of the oscillator crystal may be representedin any suitable manner, e.g. using various forms of approximatingfunctions which may deviate from the above-mentioned types ofapproximating functions or may even combine different types ofapproximating functions. Further, although the above embodimentsillustrate the oscillator element 10 as a separate component apacedapart from the electronic device 100, other embodiments could implementthe oscillator element 10 and at least a part of the oscillator circuit110 together in a separate component spaced apart from the electronicdevice 100, e.g. in an SiP component.

1-25. (canceled)
 26. An apparatus for a mobile device, the mobile devicecomprising: a crystal configured to generate a reference frequency; atemperature sensor configured to generate indications of a temperatureof the crystal; and a processor configured: to monitor the indicationsfrom the temperature sensor, to estimate a temperature of the crystalusing the indications, to calculate a frequency change of the referencefrequency based on the estimate of the temperature of the crystal; tocompensate the reference frequency for frequency drift using thefrequency change to provide a compensated reference frequency; and toprocess data signals using the compensated reference frequency.
 27. Theapparatus of claim 26, including an analog-to-digital converterconnected to the sensor and configured to provide digital indications ofa temperature of the crystal.
 28. The apparatus of claim 26, including apositioning receiver configured to wirelessly receive positioninformation from a satellite-based positioning system and to provide theposition information to the processor.
 29. The apparatus of claim 26,wherein the processor includes a baseband oscillator configured toreceive the compensated reference frequency and to generate atemperature compensated baseband signal.
 30. The apparatus of claim 29,wherein the baseband processor includes a mobile communication systembaseband oscillator.
 31. The apparatus of claim 26, wherein atemperature drift of the crystal is based on a first indication and asecond indication.
 32. The apparatus of claim 26, including a frequencydrift configured to estimate a frequency drift of the oscillator signalbased on the temperature drift of the crystal.
 33. The apparatus ofclaim 32, wherein the frequency drift estimator is configured toestimate the frequency drift using a stored temperature characteristicof the oscillator signal frequency.
 34. The apparatus of claim 33,wherein at least a part of the stored temperature characteristic isstored in the form of parameters of an approximating function to thetemperature characteristic.
 35. The apparatus of claim 33, includingupdate logic configured to adapt the stored temperature characteristicon the basis of measured values of the indications and correspondingevaluated frequency values of the crystal.
 36. An apparatus for a mobilecommunication device, the apparatus comprising: a crystal configured toprovide a reference frequency; a temperature sensor configured toprovide temperature indications of a temperature of the crystal; awireless communication processor configured: to monitor the temperatureindications, to calculate a frequency change of the reference frequencybased on a difference between first and second temperature indicationsof the temperature indications; and to compensate the reference signalfor frequency drift of the crystal using the frequency change to providea compensated reference frequency; and to process data signals using thecompensated reference frequency.
 37. The apparatus of claim 36, whereinthe wireless communication processor is configured to generate acompensation signal based on the frequency change.
 38. The apparatus ofclaim 37, wherein the wireless communication processor includes aphase-lock loop (PLL) configured to receive the reference frequency andthe compensation signal and to provide a first compensated frequencysignal.
 39. The apparatus of claim 38, wherein the compensation signalis configured to adjust a divider of the PLL.
 40. The apparatus of claim36, wherein the wireless communication processor is configured toestimate the frequency drift based on a stored temperaturecharacteristic of the oscillator signal frequency.
 41. The apparatus ofclaim 40, wherein at least a part of the temperature characteristic isstored in the form of parameters of an approximating function to thetemperature characteristic.
 42. The apparatus of claim 36, wherein thewireless communication processor is a Universal MobileTelecommunications System (UMTS) processor.
 43. The apparatus of claim36, wherein the wireless communication processor s a global positioningsystem processor.
 44. At least one machine readable storage medium,comprising a plurality of instructions adapted for compensatingtemperature related frequency shift of a crystal, wherein theinstructions, responsive to being executed with processor circuitry of amachine, cause the machine to perform operations that: monitortemperature indications of the crystal, the temperature indicationsreceived from a temperature sensor; estimate a temperature of thecrystal using the temperature indications; calculate a frequency changeof a reference frequency of the crystal based on the estimate of thetemperature of the crystal; compensate the reference frequency using thefrequency change to provide a compensated reference frequency; andprocess data signals using the compensated reference frequency.
 45. Themachine readable storage medium of claim 44 wherein the operations thatcause the machine to calculate a frequency change include operations tocalculate the frequency change of the reference frequency based on adifference between first and second temperature indications of thetemperature indications
 46. The machine readable storage medium of claim44, wherein the operations that cause the machine to calculate afrequency change include operations to estimate the frequency changeusing a stored temperature characteristic of the crystal signalfrequency.
 47. The machine readable storage medium of claim 46, whereinat least a part of the stored temperature characteristic is stored inthe form of parameters of an approximating function to a temperaturecharacteristic.